Flotation columns are being increasingly used in the froth flotation concentration of minerals. In column flotation, a suspension of finely divided ore, containing mineral and gangue particles, is injected together with reagents into a column, usually about one quarter of the way down from top of the column, air is injected into the lower portion of the column to form a multitude of small air bubbles, and washwater is distributed into the top of the column to wash down entrained gangue particles. The froth containing the mineral particles is recovered from the top, and gangue is removed from the bottom of the column.
The air is preferably injected in the form of aerated water that may contain reagents such as frothers. The bubbles should rise uniformly across the cross section of the column. To effect this, devices, such as spargers, injectors, aspirators, nozzles and bubble generators, may be used. The preferred air bubble size in the column is related to the size of the ore particles being treated. Generally, small uniformly-sized bubbles are required to effectively float fine mineral particles, smaller than about 150 microns. To form small bubbles of uniform size, the air and water are usually ejected from the above-named devices under a relatively high pressure such as in the range of 300-700 kN/m.sup.2.